Stabilized reconstituted tobacco foil



United States Patent 3,310,057 STABILIZED RECONSTITUTED TOBACCO FOILAlbert B. Savage, Midland, and Julius C. Aldrich, Mount Pleasant, Mich,assignors to The Dow Chemical Company, Midland, Mich, a corporation ofDelaware No Drawing. Filed Apr. 30, 1964, Ser. No. 363,974 12 Claims.(Cl. 131-15) This invention relates to a process for stabilizing tobaccoagainst discoloration during the manufacture of reconstituted tobaccofoil and to the resulting tobacco product. More particularly it relatesto pretreatment of tobacco with a liquid, hydrophobic polyoxypropyleneor polyoxybutylene polyol to protect tobacco from direct contact withwater during the manufacturing process. In a preferred embodiment, thehydrophobic polyol also contains an added antioxidant. The resultingreconstituted tobacco foil retains the light color of the originaltobacco leaf and is suitable for use as an outer wrap for cigars,cigarillos, and similar tobacco products.

Numerous methods have been suggested for preparing reconstituted tobaccofoils from finely divided or pulverized tobacco particles unsuitable fordirect use in tobacco products. Such reconstituted foils must meet thegeneral test of acceptability in taste and burning characteristics aswell as have adequate physical properties such as tensile strength,dimensional stability and moisture retention. In addition, it is highlydesirable, particularly for cigar outer wrappers, that the reconstitutedtobacco, film retain the light color of the original tobacco.

Although aqueous binder systems offer many advantages in the manufactureof reconstituted tobacco foil, the sensitivity of tobacco to water posesa serious problem to their commercial use. Not only does tobacco darkenwhen wet with water, but the dark color remains upon drying and rendersthe tobacco unsuitable for use as an outer wrap. To overcome thisproblem, organic-soluble binder systems have been recommended in spiteof the hazards associated with the use of volatile organic solvents. Forexample, in United States Patent 2,893,400 Detert and Buchholz describethe manufacture of tobacco foils using an organic solution of a highlysubstituted, organic-soluble methyl cellulose as a binder. Yet even withthis system, accidental traces of water result in noticeablediscoloration of the tobacco foil. Hence a simple and effective meansfor protecting the tobacco from direct contact with aqueous orwater-containing process solutions while retaining desirable physicaland smoking qualities is a useful advance in the art of preparingreconstituted tobacco foil.

It has now been discovered that tobacco can be protected from darkeningthrough contact with water by pretreatment with a hydrophobic, liquidpolyoxyalkylene diol or triol characterized by:

(1) A solubility in water of less than about 2 weight percent at 25 C.,

(2) A viscosity of 100 to 1,200 centistokes at 25 C., and

(3) An average molecular weight of from 500 to 5,000.

The resulting treated tobacco has enhanced color stability duringmanufacture of a reconstituted tobacco foil using a water-solublebinder. This enhanced color stability of the tobacco in contact withwater is also advantageously retained by the final reconstituted tobaccoproduct.

It has further been discovered that incorporation with the polyol duringthe pretreatment of the finely divided tobacco of an antioxidant in anamount suflicient to inhibit oxidation during processing permits morerapid drying of the reconstituted tobacco foil without discoloration.

3,310,057 Patented Mar. 21, 1967 Particularly suitable are stericallyhindered alkylphenol antioxidants approved for food and drug use.

Treatment of the tobacco in the manner described herein does notdelete-riously aflFect the strength of the reconstituted tobacco foil.The polyoxyalkylene polyols used are compatible with many bindersgenerally employed in the preparation of reconstituted tobacco foil.They are essentially non-toxic and in the amounts used do not detractfrom the burning characteristics, flavor or other desired properties ofthe tobacco. While this pretreatment is particularly advantageous when awater-soluble binder is employed, it can also be used withorganic-soluble binder systems wherein small amounts of water may beencountered.

Critical to the present invention is the pretreatment of the tobaccowith a liquid polyoxyalkylene polyol having only limited watersolubility. In practice, polyols having a solubility of 2 percent orless in water at 25 C. are satisfactory. Furthermore, to achieve readyintermixing and coating of the tobacco particles without use of asolvent or diluent, the liquid polyols should have a viscosity of about-1,200 centistokes at 25 C. These properties are obtained withcommercial polyoxyalkylene polyols prepared by condensation of propyleneoxide and/ or 1,2-butylene oxide with appropriate initiators, such aswater, glycerine, propylene glycol, etc. Particularly suitable arepolyoxyalkylene diols or triols characterized by the formula:

In{(OCH CHR) OH?r wherein In is the polyol initiator, R is a C -C alkylgroup, In is 2 or 3, and n is the number of oxyalkylene units per polyolchain.

Although the necessary water insolubility is achieved withpolyoxybutylene polyols having an average molecular weight as low as500, with polyoxypropylene polyols the average molecular weight must begreater than about 1,000 to achieve the required degree of waterinsolubility. Since it has been found that higher molecular weightpolyols may also improve the strength of the reconstituted tobacco foil,polyols having a molecular weight in the range from 1,500 to 5,000 areparticularly desirable. Block or heteric copolymers of propylene oxideand 1,2- butylene oxide may also be used if they have the proper waterinsolubility and viscosity.

The amount of polyol necessary for satisfactory pretreatment of thetobacco depends particularly on such factors as the particle size andsurface area of the to bacco. However, in general from 5 to 30 weightpercent and preferably about 10 to 20 weight percent, tobacco basis, ofthe polyol is incorporated with the finely divided tobacco, preferablyby spraying and dry mixing. Other means for obtaining a surface coatingof the polyol on the tobacco particles can also be used includingtreatment with a solution of the polyol in a volatile solvent such asmethanol. Conventional tobacco additives, such as combustion aids orretardants can also be incorporated with the polyol-treated tobaccobefore blending with the binder.

As a further modification of the present invention, it has beendiscovered that addition of a small amount of a suitable antioxidantwith the polyol used to pretreat the tobacco prior to mixing with thebinder, results in enhanced color stability during the processing anddrying of the resulting tobacco foil. The improved stability isparticularly advantageous in permitting more rapid drying and higherdrying temperatures without detrimental' discoloration.

In practice the sterically hindered phenolic antioxidants approved forfood and drug use, such as butylated hydroxyanisole (BHA), butylatedhydroxytoluene (BHT), nordihydroguiairetic acid (NDGA) and phenylsalicylate (salol), are preferred. Other commercial primaryantioxidants, such as Santinox R or N-lauryl-paminophenol, are alsosuitable. Such food stabilizers as ascorbic acid, gallic acid, citricacid and malic acid are not effective at a practical concentration levelalthough they may be present as minor components of suitable antioxidantcompositions. The effective antioxidants are also generallywater-insoluble but soluble in the hydrophobic polyols used to pretreatthe tobacco. Thus they are readily incorporated in the pretreatedtobacco by addition with the desired polyoxyalkylene polyol.

The effectiveness of the antioxidant is influenced by the nature of thepolyol. For example, less antioxidant is required when a polyoxybutylenediol is used rather than a similar molecular weight polyoxypropylenediol. However, in general, a suitable antioxidant must be effective at aconcentration of from about 100 to 5,000 p.-p.m. based on the weight oftreated tobacco. Within these limits, the preferred antioxidant andoptimum concentration for a particular system can be determined byroutine tests.

It has still further been noted that if the aqueous process solutionsare contaminated with copper, iron or other heavy metal ions whichpromote oxidative discoloration of the tobacco, a suitable chelatingagent such as calcium disodium ethylenediaminetetraacetate, disodiumethylenediaminetetraacetate, or sodium hexametaphosphate may be used toobviate their effect.

The invention disclosed herein is particularly advantageously used inconjunction with the process described by Savage and Aldrich in UnitedStates patent application Ser. No. 361,221, filed on Apr. 20, 1964, forthe manufacture of reconstituted tobacco foil using an alkalisolublemethyl cellulose as the binder. The process involves intermixing finelydivided tobacco with an alkaline solution of alkali-soluble methylcellulose and extruding the resulting slurry into an acid salt coagulantbath to form a continuous, self-supporting film. When dried, theresulting tobacco foil has enhanced moisture resistance and suitabletensile strength and dimensional stability for use as a binder in thepreparation of cigars and similar tobacco products. However, the tobaccooften is darkened by contact with the aqueous process solutions and thereconstituted foil usually does not have the appearance and particularlythe light color desired :for use as an outer cigar wrap. By pretreatingthe tobacco with a hydrophobic polyol, as described herein, and thenintermixing with the alkaline methyl cellulose solution, an improvedreconstituted tobacco foil is obtained having a color comparable to thatof the original tobacco.

The invention is not limited to use with an alkalisoluble methylcellulose binder. It can be used with other water-soluble binders, forexample, carboxymethyl cellulose, hydroxyethyl cellulose, awater-soluble methyl cellulose as well as such natural products asalginates, pectins, and plant gums, to enhance the color stability ofthe tobacco. Pretreatment of the tobacco with a hydrophobicpolyoxyalkylene polyol, as described herein, can also be advantageouslyemployed when waterinsoluble binders are used if discoloration fromcontact with water is encountered during processing.

The following examples are given to illustrate further the inventiondescribed herein. Unless otherwise specified, all parts and percentagesare by Weight. oxyalkylene polyols used are commercial products preparedby the addition of alkylene oxide to a conventional initiator. Forconvenience, they are identified by a letter indicating the alkyleneoxide (Eethylene oxide; P1,2-propylene oxide; B1,2-butylene oxide)followed by a number designating the average molecular weight. Thecomparative evaluations of the tobacco color were made by an experiencedobserver.

Example 1.-Stabilized reconstituted tobacco foil (A) To a solution of 90parts of sodium hydroxide in 800 parts of water was added 53 parts ofalkali-soluble methyl cellulose (7%-OCH having a viscosity of 72 cps. asa 2% solution in 6% NaOH at 20 C., 4 parts of a liquid polyoxyethyleneglycol (M.W. 200) and 4 parts of a solid polyoxyethylene glycol (M.W.4,000). The mixture was stirred and cooled to about 0 C. Finally thecaustic solution of methyl cellulose was filtered through a 150 meshscreen and deaired.

(B) About 15 parts of Diol 13-1000, a liquid polyoxybutylene glycolhaving a viscosity of about 300 centistokes (cs.) at 25 C. was sprayedonto 159 parts of finely ground (200 mesh), light golden shade tobacco.The dry mixture was thoroughly blended by tumbling in a sealed containerto coat the tobacco particles with the glycol. Finally an aqueoustobacco slurry was made by adding 610 parts of water.

This tobacco slurry was slowly added and intermixed with the alkalinemethyl cellulose solution (A). The slurry was deaired by briefcentrifuging and then transferred to the reservoir of a film casting diehaving a 0.013" by 5" slit. By means of air pressure on the reservoir,the slurry was extruded beneath the surface of a H SO -Na SO coagulatinghath containing 16% sulfuric acid and saturated with sodium sulfate. Thecoagulated film was drawn through the bath With a contact time of about30 seconds and then washed with hot water (60 C.), neutralized in adilute sodium bicarbonate solution, rewashed with hot water and finallydried by contact with a heated steel roll having a surface temperatureof about 120 C.

The dried reconstituted tobacco foil was golden brown in color, quitecomparable to that of the initial tobacco and greatly superior to theunattractive dark brown color of a control foil prepared in the samemanner without pretreatment of the tobacco with the Diol B-lOOO. Itcontained 0.8% acid calculated as sulfuric acid but no residualinorganic sulfate. It had a thickness of about 3 mils and was flexibleand self-supporting over a wide range of temperature and relativehumidity. The tobacco foil did not darken when a drop of water was lefton its surface for several minutes. l

(C) The effect of drying conditions on the color of the reconstitutedtobacco film is illustrated in Table 1 with typical results from dryingsamples of the washed film described in 1B under several conditions. Ingeneral the best color is obtained by slow drying at ambienttemperature. At temperatures above 40-50" C. darkening frequentlyoccurs. However, if the foil has sufiicient stability to be driedrapidly at temperatures of about l10120 C., discoloration can beminimized.

TABLE 1.-DRYING- CONDITIONS Method Best, light golden. Excellent, lightgolden. Discolored, brown.

Dark brown.

The poly- Example 2.Poly0xyalkylene polyols Following the generalprocedure of Example 1, reconstituted tobacco foils were prepared usingalkalisoluble methyl cellulose as a binder for tobacco pretreated withvarious polyoxyalkylene polyols. The polyols were applied to the tobaccoas a liquid spray, or in the case of the solid Diol E-4000 as a melt oras a solution with liquid Diol E-ZOO. About -20 wt. percent of eachpolyol was used based on the weight of tobacco. After coagulation andwashing the tobacco foils were dried on a heated roll. The appearanceand color of the foils were noted and samples taken for analysis anddetermination of physical properties.

From observations such as given in Table 2 it is evident thatpretreatment with the hydrophobic polyols enhances the color stabilityof the tobacco during the was generally used as the polyol. This treatedtobacco was then slurried with an alkaline solution containing about -40parts of alkali-soluble methyl cellulose such as describedin Example 1A.From each test slurry a thin film was cast or extruded, coagul-ated in aH 80 Na SO bath, washed and dried. The effectiveness of the antioxidantswas judged by comparison of these test foils with control films preparedwithout an antioxidant.

Typical results from this antioxidant test are given in Table 3. Thesterically hindered phenolic antioxidants gave a marked improvement intobacco color retention when the foil was dried at an elevatedtemperature of up to 120 C. while citric acid, malic acid, gallic acid,dextrose and propyl gallate were ineffective. Also illustrated in Table3 is the influence of the polyol structure.

TABLE 3.ANTIOXIDANT TEST Polyol Antioxidant Observation of the DryingTobacco Foil A Diol P-1200 Phenyl salicylate. Excellent color andstability at 120 C.

d NDGA Do. BHA D0. N-lauroyl-p-aminophenol Good; improved colorstability at 120 C. p-Benzyloxyphenol..-- Do. Malic acid Poor; darkensat 100-120 C. Citric acid. Do. ...-.do Propyl gallate.-. Do. B DiolB-1000. Phcnyl salicylate Excellent color and stability at 120 C.

Diol 13-2000 ..do Superior color and stability at 120 C.

' Excellent color and stability at 120 C. Dio1E-200 .do Very poor.

processing. In general superior results were obtained with the butyleneoxide derived polyols. A definite increase in tensile strength was notedwith the B2000 foil. Trio-ls gave results generally similar to thecorresponding diol of about the same molecular weight. The foilsprepared from tobacco pretreated with water-soluble Diol P40() and theEpolyols were noticeably discolored even before drying.

Example 4.-Water-s0luble binders The effect of the hydrophobic polyolpretreatment with several different commercial water-soluble cellulosicbinders is shown in Table 4. A standard finely divided shade tobacco wasused with appropriate pretreatment with 2.5 parts of polyoxyalkylenediol and 1 part of salol per 30 parts of tobacco. To 1 part of theuntreated control tobacco or the pretreated tobacco was added 10 partsTAB LE 2.PRETREATMENT WITH POLYOXYALKYLENE POLYOLS Water Sol.,Viscosity, Polyol Wt. Pccent cs., 2 Observations of the Drying TobaccoFoil Diol 13-500 0. 1 124 Excellent color, stable at 120125 0.

0. 1 231 Do. 0. 1 553 Best color, stable at 120-125 C. -2 160 Goodcolor, darkens slowly at 120 C. Diol P-4000. 0. 1 1, 114 Ggodfi t1color,darkens slowly at 120 0.,

11 e. Triol P1030 0. 1 218 Good color, darkens slowly at 120 C.

' 00 70 Poor color, darkens at 100-120" C.

so 90 Very poor color, darkens at 100-120 C co Solid Poor color, darkensat 100120 C.

Example 3.-Anti0xidmzfs As a screening test for antioxidants to be usedwith the hydrophobic polyols in the pretreatment of tobacco, a mixtureof 10-20 parts of polyol and 1 part of antioxidant was thoroughlyintermixed with 100 parts of finely divided tobacco. For the initialtest Diol P-lZOt) TAB LE 4.WATER-SOLUB LE BINDERS Color Rating of DriedTobacco Foils Binder 1 Control 13-2000 B-2000+AO P-4000 P-4000+AOMethocel MC, 50 cps P001 Fair-good...-- Good Fair Fair. Methocel HG, 50cps...- Fair. Very good..-.. Best.. Good Good. Natrosol 250 HEC Poor...Fair-good.-." Fair Fair-good..." Fair. Ccllosize WP40 .-.-.do ..do FairPoor. CMC, 72 cps ..do do .do ..do Do.

1 Methocel MC-A methyl cellulose containing from 27.5-31.5%-OCH The DowChemical Company.

Methocel 65 HG-A mixed cellulose ether containing 27-29%OCH; and 44.5%hydroxypropyl ether;

The Dow Chemical Company.

Natrosol 250 HECA hydroxyethyl cellulose (M.S.=2.5) having a 1% aqueousviscosity of 1,500-2,500 cps.

at 25 0.; Hercules Powder Company, Inc. Cellosize WP40-A hydroxyethylcellulose (M.S.=1.6) having a 2% aqueous viscosity of 75-125 cps.; UnionCarbide Corporation.

Example .Organic-s0luble binders Using the test tobacco mixturesdescribed in Example 4, test foils were prepared using a 4% solution oforganicsoluble methyl cellulose (42.5% OCH in 70 parts benzene-30 partsmethanol. The test foils cast and dried at room temperature wereevaluated for color and then a stripe of Water was run across the filmfollowed by redrying. As shown in Table 5, the color stability of theinitial solvent cast foils is very good even with the untreated tobacco.However, when the cast foils were exposed to water and redried, theimprovement in color stability of the hydrophobic polyol treated foilswas evident.

TAB LE 5.ORGANIC-SOLUB LE BINDER Color Rating of Tobacco Foils TobaccoFoil Dried at G.

Control B-2000 B2000+AO P-4000 P-4000+AO Solvent cast Very good Verygood Ve1ygood Excellent Excellent. Water-striped 25 Poor.. .d Fair" FairPoor.

Do 100 .-.do Fair- Fair-good "do Fair-poo1z We claim: 25 (2) a viscosityof 100 to 1,200 centistokes at 25 1. In a process for the preparation ofa reconstituted tobacco foil from finely divided tobacco and acellulosic binder wherein the tobacco and cellulosic binder areintermixed in the presence of water, the improvement whereby the tobaccohas enhanced color stability during manufacture of the reconstitutedtobacco foil which comprises:

(A) Treating 100 parts of finely divided tobacco with from about 2 toparts of a liquid polyoxyalkylene polyol wherein the oxyalkylene groupsare oxypropylene and/ or oxybutylene groups and characterized by: (1) awater solubility of less than about 2 weight percent at 25 C., (2) aviscosity of 100 to 1,200 centistokes at 25 C., and (3) an averagemolecular weight of from about 500 to 5,000; and

(B) Intermixing therewith the cellulosic binder and forming areconstituted tobacco foil.

2. The process of claim 1 wherein the binder is an alkali-soluble methylcellulose having a degree of substitution from 0.2 to 0.7.

3. The process of claim 1 wherein the binder is a watersoluble methylcellulose.

4. The process of claim 1 wherein the binder is a watersolublehydroxyethyl cellulose.

5. The process of claim 1 wherein the binder is a watersolublecarboxymethyl cellulose.

6. The process of claim 1 wherein the polyol is a polyoxybutylene diol.

7. The process of claim 1 wherein the polyol is a polyoxypropylene diolhaving an average molecular weight in the range from 1,000 to 5,000.

8. The process of claim 1 wherein from about 100 to 5,000 p.p.m. of asterically hindered phenolic antioxidant References Cited by theExaminer UNITED STATES PATENTS 2,893,400 7/1959 Detert et al 131-152,927,588 3/1960 Detert et a1 131-l5 2,971,517 2/1961 Pihl 131-15References Cited by the Applicant UNITED STATES PATENTS 2,797,689 7/1957Frankenburg.

OTHER REFERENCES W. O. Lundberg: Autoxidation and Antioxidants, vol.

IL, Interscience, New York, 1962, Ch. 11.

E. Ott et al.: High Polymers, vol V., Cellulose and CelluloseDerivatives, 2nd ed., New York, 1954, part II, Ch. 1X.

SAMUEL KOREN, Primary Examiner.

MELVIN D. REIN, Examiner.

1. IN A PROCESS FOR THE PREPARATION OF A RECONSTITUTED TOBACCO FOIL FROMFINELY DIVIDED TOBACCO AND A CELLULOSIC BINDER WHEREIN THE TOBACCO ANDCELLULOSIC BINDER ARE INTERMIXED IN THE PRESENCE OF WATER, THEIMPROVEMENT WHEREBY THE TOBACCO HAD ENHANCED COLOR STABILITY DURINGMANUFACTURE OF THE RECONSTITUTED TOBACCO FOIL WHICH COMPRISES; (A)TREATING 100 PARTS OF FINELY DIVIDED TOBACCO WITH FROM ABOUT 2 TO 30PARTS OF A LIQUID POLYOXYALKYLENE POLYOL WHEREIN THE OXYALKYLENE GROUPSARE OXYPROPYLENE AND/OR OXYBUTYLENE GROUPS AND CAHRACTERIZED BY: (1) AWATER SOLUBILITY OF LESS THAN ABOUT 2 WEIGHT PERCENT AT 25*C., (2) AVISCOSITY OF 100 TO 1,200 CENTISTOKES AT 25* C., AND (3) AN AVERAGEMOLECULAR WEIGHT OF FROM ABOUT 500 TO 5,000; AND (B) INTERMIXINGTHEREWITH THE CELLULOSIC BINDER AND FORMING A RECONSTITUTED TOBACCOFOIL.